While great efforts have been made to prevent large oil slick and asphalt-like substances from entering into the Louisiana coastal water system, it is the dispersed oil and dispersant residual that may get into the estuaries and present an even greater and long term threat to the Louisiana coastal ecosystem. Though the federal government has ordered BP to limit the dispersant usage, it is estimated that more than two million gallons, a record high amount of dispersants, has been used .
Due to its small droplet size and increased mobility, dispersed oil has much higher chance to enter the coastal and inland water system due to tides, winds and waves. The negative impact from these oil droplets along with dispersant residuals is almost inevitable [2-4]. The health of the Louisiana wetland and fishery is especially vulnerable to the sudden increase of the hydrocarbon concentration in the water. The long-term environmental impact of the dispersants and dispersed oil has not been well studied and has remained a controversial topic.
In addition, the spilled oil tends to dissolve faster in seawater environment than in fresh water. Along the north Gulf Coast, there are vast areas of marshes and wetlands with low salinity. This makes it more difficult for any oil in it to dissipate and dissolve. It is therefore very important to keep monitoring the leaked oil in the coastal water system, especially wetlands, and gather valuable information not only for the evaluation of the impact of this oil spill disaster, but also for building up a database for future studies of the long term effect of dispersed oil and dispersant on the wetland ecosystem.
The crucial question is whether the dispersed oil has drifted or transported into estuaries and wetlands although the dispersants were used in the offshore deep water. To answer such a question, new oil detection instruments are needed. The special requirements for a new device include 1) high accuracy as the oil concentration may not be detectable using existing instruments; 2) small and portable as access to wetlands is difficult; and 3) easy to operate as the environmental monitoring of a vast coastal areas need many volunteers with very limited training or measurement skills.
However, the existing technology cannot meet these requirements. For example, U.S. coast guard has used Tuner 10AU field fluorometer (Turner Design Inc., Sunnyvale, CA) in the Gulf of Mexico. The device is bulky (13.39 in. X 21.65 in, weight – 34.5 lbs) and also requires various accessories such as pump cables, power supply etc. Though there are also some newer and smaller commercial oil detection products, they tend to offer much lower sensitivity than what may be needed for monitoring spilled oil droplets in the coastal water.
We propose to develop a highly sensitive and portable oil concentration monitoring system with a lab-on-chip microfluidic system with integrated micro-optical detection function in it. The microfluidic system will serve the function of sample (oil in water) extraction, pre-concentration. The sample acquisition will be accomplished by utilizing an on-chip peristaltic micro-pump and thus eliminate the requirement of external pumping and accessories. The on-chip micro-optical oil detection unit is based on fluoresce detection principle. With the aid of a microfluidic pre-concentration unit, we aim to reach ppb (part per billion) level detection limit. The lab-on-chip oil detection system makes it feasible to obtain a compact hand-held unit without external power supply and with minimum accessories.
The goals of this proposal in the one year period are to conduct research on several key scientific and technological issues involved, which include a microfluidic liquid-liquid extraction unit for sample pre-concentration, an on-chip fluorescence detection unit with fiber optics, an off-chip light source unit and high sensitivity optical detection unit, and an easy-to-operate user interface for result display and normal operation. The proposed project may result in a novel mTAS technology for on-site monitoring of spilled oil in water column, not only for the oil accident in the Gulf of Mexico, but also for other commonly happened oil leakage in pipelines across the country. The on-chip sample pre-concentration and integrated optical detection technology can also be used in other applications.